This application is a continuation of international patent application no. PCT/EP00/05598, filed Jun. 17, 2000, designating the United States of America, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany patent application no. DE 199 33 040.9, filed Jul. 15, 1999.
The invention relates to a free-jet centrifuge suitable, for instance, for cleaning the lubricating oil in an internal combustion engine.
Freejet centrifuges of this type are known in the art. German Utility Model application no. DE 296 09 980 U1 proposes a rotor of a centrifuge suitable for mass production in large numbers. It comprises a plurality of sheet metal cups that are connected by common flanging (see FIG. 1 of the cited document). This unit has a center tube 30 into which sleeves 31, 32 are inserted. These sleeves rotatably support the centrifuge rotor on a housing shaft 16 and limit the axial play of the rotor within the clearance. During operation, the rotor can move back and forth between the axial limits of the housing. Due to the oil pressure and any downward tilt of the nozzles 28, the rotor tends to rise inside the housing.
If the oil pressure drops below a predetermined value, valve 40 closes, thus preventing the oil from passing through the centrifuge rotor. Due to bearing friction of the slide bearings, the rotor then comes to a stop. Bearing friction is increased because the centrifuge rotor is lowered to the lower axial limit stop within the housing, which increases the bearing surface of the slide bearing.
Despite the use of integrated components, e.g., pressure valve 40, the described rotor module is highly complex. This makes it difficult to produce the rotor in an economical manner. In particular, the axial position of the rotor is not precisely defined during operation. Sudden pressure fluctuations can, for instance, cause the rotor to strike against one of the axial limit stops even during operation. As a consequence, these limit stops must be equipped with similarly favorable frictional properties as the radial area of the slide bearings.
A further problem is the run-on behavior of the centrifuge when the oil supply is interrupted. In such a case, the centrifuge should come to a stop as quickly as possible. The kinetic energy of the rotor is reduced through bearing friction. To obtain the highest possible rotational speeds, however, bearing friction should be as low as possible. In other words, the more successful the reduction of bearing friction, the longer the centrifuge will run on.
If oil centrifuges are used in passenger cars, the requirements for smooth running characteristics of the engine are particularly high. At the same time, frequent load variations, e.g., if the car is used in densely populated areas, cause the centrifuge to be continuously turned on and off. When the internal combustion engine is idling, long run-on of the centrifuge rotor is unacceptable due to noise, since it is louder than the quiet engine noise in this operating state and is perceived as disagreeable by the driver.
The object of the invention is to provide an improved centrifuge with a rotor that achieves a good centrifuge result by realizing high rotational speeds
A further object of the invention is to provide a centrifuge with a rotor which has short run-on times after being turned off.
These and other objects have been achieved in accordance with the present invention by providing a free-jet centrifuge comprising a rotor having an oil inlet, at least one drive nozzle as an outlet, and a deposition surface interiorly of the rotor; a housing in which the rotor is rotatably disposed to shield the rotor against the environment, and bearing means for rotatably supporting and limiting the axial play of the rotor inside the housing; in which a fixed, externally actuated power source is provided on the free-jet centrifuge, the power source exerting a force which acts on the rotor in an axial direction counter to axial forces created by rotor operation, the power source being dimensioned such that the centrifuge can be pushed against the axial play limit by actuation of the power source to brake the centrifuge from any operating state.
In accordance with a further aspect of the invention, the objects are achieved by providing a rotor for use with a free-jet centrifuge comprising a housing in which the rotor is rotatably mounted to shield it from the environment, the rotor comprising an oil inlet, at least one drive nozzle as an outlet, a deposition surface interiorly of the rotor, and rotor bearing means for engagement with mating housing bearing means to rotatably mount the rotor in the housing; wherein the rotor bearing means interacts with the housing bearing means to limit axial play of the rotor within the housing; and the rotor comprises a rotor friction surface outside the rotor bearing means for engagement with a housing friction surface to brake the rotor upon actuation of a power source.
The free-jet centrifuge according to the invention comprises a rotor with an inlet and at least one drive nozzle, which simultaneously serves as the outlet. The deposition surface for the separated suspended solids contained in the fluid is formed, for instance, by the rotor shell. The housing shields the rotor against the environment. This is necessary because the spray of the drive nozzles must be collected. Within the scope of the invention the term xe2x80x9chousingxe2x80x9d should be understood to refer to any type of casing protecting the environment. It is not necessary to provide a separate housing for the centrifuge. It is also feasible, for instance, to build the centrifuge into cavities of an internal combustion engine that forms part of the oil circuit. The support of the centrifuge rotor inside the housing simultaneously allows its rotation and limits its axial play.
According to the invention the free-jet centrifuge is provided with a power source, which is fixed inside the centrifuge housing and the force of which acts on the rotor. This power source can, for instance, be a prestressed helical spring, the ends of which are supported on the rotor bearing and on the housing, respectively. The force of the power source acts against the axial forces created during rotor operation. As a result, an equilibrium of forces is established between the power source and the rotor in operation. The rotor, within its axial range of movement, migrates into the position of this equilibrium of forces without contacting either of the axial limit stops. This permits low-friction operation of the centrifuge at high rotational speeds. The power source simultaneously acts as a buffer when there are pressure fluctuations that shift this equilibrium of forces, but it does not cause the rotor to rub against one of the axial limit stops.
As soon as the oil pressure falls below a certain value, the power source pushes the rotor against one of the axial limit strops. This creates a braking torque, which is capable of braking the rotor until it comes to a stop. Prolonged run-on is prevented, so that there are no audible running noises of the centrifuge, e.g., when the internal combustion engine is idling. The power source further has the positive effect that the bearing partners are kept under tension. As the centrifuge continues to rotate, this prevents knocking of the bearings due to the bearing play, which can also cause a disagreeable noise. Furthermore, the risk of bearing damage due to knocking, which shortens the life of the bearings, is avoided. This is necessary particularly if roller bearings are used to support the rotor. But slide bearings also benefit from the decreased run-on times. Due to the low oil pressure in this operating state, lubrication of the bearings is no longer fully assured. Prolonged run-on would therefore cause increased bearing wear.
Normally, the external support by the power source will act in the direction of the gravitational force. This has to do with the typical installation position of oil centrifuges. In prior art centrifuges, the force of gravity is the necessary counter force for the axial forces created in rotor operation. The use of the described power source, however, eliminates the need for a vertical installation position utilizing the gravitational force of the rotor. It can be completely replaced by the power source, so that it is possible, for instance, to install the rotor with a horizontal axis of rotation. This provides greater freedom of design when using a free-jet centrifuge, e.g., in an internal combustion engine.
If a spring is used as a power source as described, the spring exerts a force which depends on the axial position of the rotor within the housing in accordance with the characteristic curve of the spring. This is a particularly simple embodiment, which creates a self-regulating system for the free-jet centrifuge. A prerequisite, however, is that the spring is configured in such a way that the amount of the spring force is always less than or equal to the amount of the axial force created by rotor operation within the intended operating range. The operating range is defined by the rotational speed of the rotor and the oil pressure. Only below this operating range does the spring force exceed the axial force of the rotor, so that the rotor is pushed against one of its axial limit stops and is braked. When the oil pressure increases, the acceleration behavior of the rotor is ensured because the rotor can disengage again from the axial limit stop and be set into rotation. It then moves axially against the spring force until the described force equilibrium is reestablished. This self-regulating configuration can of course also be achieved with other power sources, e.g., a pneumatic cylinder.
Another advantageous option is to provide the power source with external actuation. This makes it possible to use any control mechanism to control the force applied by the power source. The power source can, for instance, comprise an externally controlled hydraulic cylinder. As an alternative, an electromechanical drive, e.g., a motor-gear combination may be used. The pressure capsules frequently used in the automotive field are also a feasible solution for the externally actuated drive of the power source.
With the aid of external actuation, the centrifuge can be braked from any operating state by being pushed against the axial limit stop when the power source is activated. Operating states in which braking of the rotor is appropriate are the previously described idling state as well as any impending insufficient lubricating oil supply of the internal combustion engine. In such a case, the externally actuated power source can turn off the centrifuge, so that the bypass flow of oil necessary to operate the centrifuge is available directly for lubrication. This function is normally assured through appropriate valves in the oil circuit, which can be omitted in the present invention. This provides additional savings that increase the economic efficiency of the invention or compensate the additional costs for the externally actuated power source.
A particularly advantageous embodiment is obtained if the free-jet centrifuge is equipped on one side with a slide bearing or plain friction bearing, which simultaneously acts as an inlet. In this case, the inflowing liquid provides lubrication. The second bearing used is a roller bearing, which has extremely low friction losses. The roller bearing is mounted completely outside the liquid stream to be centrifuged. The power source is clamped between a support inside the housing and the roller bearing, so that the roller bearing is axially displaceable. As the roller bearing is displaced, the centrifuge rotor is simultaneously moved. The slide bearing permits this axial movement. The roller bearing can, for instance, be fixed to the rotor with its inner race, whereas the power source engages with the outer race. This prevents any roller bearing play irrespective of the operating state of the centrifuge.
An alternative means for braking the rotor is to utilize a thrust reversal. This is accomplished by actuating nozzles on the centrifuge rotor, which enable a drive in the opposite direction of the normal direction of rotation. To this end, the nozzle heads of the centrifuge rotor may be rotatable, so that the thrust reversal is achieved by rotating the nozzles 180xc2x0. Another option is to mount additional braking nozzles, which spray in opposite direction of the drive nozzles. The pressure inside the rotor can be used to control the nozzles.
Another alternative embodiment of the invention provides for a friction surface pair outside the bearing means. One of the friction partners is fixed inside the housing and the other on the rotor. This friction surface pair can be used as a brake. It is advantageous to make the friction partners ring-shaped and to accommodate them in the area of one of the rotor axial end surfaces and the housing. The function of this friction surface pair is comparable to the above-described axial limit stop of the bearing. The friction surface pair replaces precisely this axial limit stop in the bearing, namely the one in the direction opposite the rotor""s tendency of axial movement in operation. Outside the intended operating range of the rotor, the rotor is lowered onto the friction pairing and is thereby braked. This process can be supported by a power source in accordance with the invention. Alternatively, this effect can also be achieved solely by the gravitational force acting on the centrifuge rotor.
Decoupling the braking function and the bearing function makes it possible to select the ideal material pairs for the two tasks. Attention can be focused on minimizing friction losses in the design of the bearing and on maximizing the braking torque in the selection of the friction pairing for braking. Furthermore, the friction partners can be installed near the outer periphery of the rotor to further enhance the friction torque through their geometric arrangement. The following materials are particularly suitable for friction pairing to brake the rotor. The material of the one friction partner may advantageously be polyamide (PA), optionally reinforced with glass-fibers, polyoxymethylene (POM), or polytetrafluoroethylene (PTFE). The material for the other friction partner may advantageously be PA, POM or PTFE, or bronze, steel or an aluminum alloy.
In another advantageous embodiment of the invention, a brake band is arranged inside the housing. This brake band can, for example, interact with the lateral surface of the rotor. The desired braking effect can be achieved by tightening the brake band.
Providing the described means for braking the rotor, be it additional friction pairs or power sources to increase the friction in the bearings, makes it possible to brake the rotor to a full stop from any operating state. This makes it possible to minimize the flow through the centrifuge, since the volumetric flow rate at the nozzles reaches appreciable values only at high rotational speeds due to the dynamic pressures created in the interior of the centrifuge. At zero speed the volumetric flow rate through the narrow nozzle bore is negligible. This completely eliminates the need for valves to actuate and control the centrifuge. The leakage flow through the nozzle opening at zero-speed of the rotor is acceptable. Eliminating the control valves clearly increases the economic efficiency of the centrifuge.
These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either alone or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed.